The present invention relates to a process for the production of pure neohexanol having a purity, for example determined by gas chromatography, of above 99.0% and with chlorine and sulfur contents of less than 10 and 5 ppm, respectively. The process involves esterification of a dimethylbutyric acid low in chlorine with an alcohol boiling above 117.degree. C.; purification of the ester by distillation; and subsequent catalytic hydrogenation to the alcohol.
Syntheses of neohexanol are described in the literature, such as, for example, in U.S. Pat. Nos. 2,481,157 and 2,481,158. These propose a reaction of vinyl chloride with tert-butyl chloride in a pressurized reactor. In this process, a chlorine compound is obtained as an intermediate product in moderate yield. Hydrolysis of the intermediate product under pressure produces neohexanal. One disadvantage in this process is the high technical expenditure, the low yield, and the inadequate purity of the aldehyde. The high chlorine content of far above 10 ppm causes especially great problems during the further processing of the aldehyde. For example, the aldehyde cannot be reduced to neohexanol by catalytic hydrogenation due to corrosion and catalyst poisoning derived from the chlorine content.
In a two-stage process for the production of neohexanol (German Patent 925,229=British Pat. No. 693,390), ethylene and isobutene are reacted with 95.5% strength sulfuric acid at -15.degree. C. and under about 10 bar. The resultant sulfuric acid esters are hydrolyzed to the alcohol in a second stage. This method is technically expensive due to the required pressure, the low temperatures, and the corrosive medium, and results in relatively low yields of at most 60 polar percent.
Ipatieff et al (Journal of American Chemical Society 73: 553 [1951]) suggests a synthesis of neohexanol from 1-chloro-3,3-dimethylbutane by heating with aqueous potassium carbonate solution to 230.degree. C. In this process also, the yield is low, i.e. 65%, and the technical expenditure is very high due to the corrosive medium and the high temperatures. Furthermore, the chlorine compound employed is hard to manufacture industrially because its synthesis, by the so-called Schmerling method (Journal of American Chemical Society 67: 1152 [1945]), requires low temperatures, for example of -60.degree. or -40.degree. C.
In contrast, a process wherein 3,3-dimethylbutyric acid is reduced with lithium aluminum hydride in ether provides a yield of 83.5% (Sarel, Newmann, Journal of American Chemical Society 78: 5416, 5417, 5419 [1956]). This mode of operation involves a method suitable only for the preparation of small amounts (up to 1 kg) of neohexanol in a laboratory. As for this reaction, another reducing method using sodium and ethanol (Sutter, Helv. 21: 1259 [1938]) is likewise unsuitable for industrial application on account of the high costs for the starting material.
All of the conventional processes, therefore, produce only low yields, require expensive technical apparatus, result in an unclean product, or utilize chemicals which are expensive and, due to the way they must be handled, are suitable only for laboratory work.
Thus, there is still great interest in finding a process enabling the production of a very pure neohexanol with a content of above 99.0%, in high yield with minor technical expenditure.